Service providers are able to provide numerous voice and data services to end users (also referred to as subscribers, user equipment, wireless devices, etc.). Examples of voice services are voice calls, call forwarding, call waiting, etc. Examples of data services are streaming audio, streaming video, Voice over Internet Protocol (VoIP), online gaming, IP-TV, etc. The data services are managed by a Packet-Switched (PS) core network, which interfaces the end user with one or more external Packet Data Networks (PDN), such as the Internet. When accessing data services, the sessions established by end users are typically much longer in duration than traditional voice calls. For instance, a typical voice call may last ten minutes or less, while data sessions for surfing the Internet, watching IP-TV, playing online games, etc., may last for many hours or even days.
PS core networks, such as the Evolved Packet Core (EPC), allow end users to engage in data sessions that are “always on”. “Always-on” sessions may be active over the PS core network for several hours or several days. Although the session is active, there may be idle periods where the end user's device is not sending or receiving data. For example, if an end user is logged into an online game, a session will be active while the end user is logged in. But, the end user may not play the game continuously when logged in, so consequently there will be idle periods during the gaming session where the end user device is not actually consuming data.
End users that are served by a PS core network may subscribe to offline charging. Offline charging refers to a charging method where charging information for network resource usage is collected concurrently with the resource usage. When network elements in the PS core network provide services for a session, the network elements are configured to report charging events to an Offline Charging System (OFCS) when certain trigger conditions are met. Some examples of triggers for charging events are data volume limits and time limits. For a data volume limit, a charging event is triggered if the volume of downlink data and/or uplink data for an end user exceeds a maximum. For example, the downlink limit may be 100 MB, and the uplink limit may be 10 MB. For the time limit, a charging event is triggered if a time limit has expired since the last charging event. For example, the time limit may be 15 minutes. Other types of trigger conditions may be specified, such as described in 3GPP TS 32.251.
When trigger conditions are detected, the network element reports the charging event to the OFCS in the form an accounting request, such as a Diameter Rf Accounting Request (ACR). The OFCS then generates Charging Data Records (CDR) for the each of the network elements based on the accounting requests that are received. At some point in time, the OFCS passes the CDRs to the billing domain where a bill is generated at the end of a billing cycle (e.g., a monthly billing cycle). The network operator can then send out a bill to the end user that specifies the usage by the end user during the billing cycle.
Unfortunately, sessions that are “always on” can cause problems to network operators when charging for these sessions.